Missing documentation relating to the 1970 Arms Trial has been uncovered showing that controversial deletions from a key witness statement were made by the prosecution legal team before the trial.
The discovery disproves suggestions made in recent years that the changes - to a statement by the former head of Military Intelligence, Col Michael Hefferon - could have been made by the minister for justice at the time or his senior officials without the knowledge of the prosecution in the trial.
The controversial deletions from the statement served to make it consistent with the evidence of the star prosecution witness, the minister for defence, Mr Jim Gibbons.
The Minister for Justice, Mr McDowell, has written this week to parties involved in the trial outlining the new discovery. He concludes that the alterations "were not carried out by the Department of Justice or its Minister but, on the contrary, by the legal team which prepared the Book of Evidence".
The minister for justice in question, Mr Desmond O'Malley, subsequently became co-founder and leader of Mr McDowell's party, the Progressive Democrats.
In the 1970 trial five defendants - two former ministers, Mr Charles Haughey and Mr Neil Blaney, an Army intelligence officer, Capt James Kelly, a Belfast republican, Mr John Kelly, and an arms dealer, Mr Albert Luykx - were acquitted of charges of attempting illegally to import weapons to arm Northern nationalists.
Mr McDowell says in his letter that some of the amendments to Col Hefferon's witness statement - arguably the majority - were made on grounds of hearsay and relevance. "Others, however, might be more plausibly explained by an editorial policy to make Col Hefferon's statement appear more compatible with that of other prosecution witnesses and, in particular, the testimony of James Gibbons TD". No evidence has emerged explaining who decided that the statement be altered in order to protect Mr Gibbons's credibility.
The most significant new document was found by officials in the office of the Attorney General in recent months. It is a typed copy of the original statement to gardaí by Col Hefferon in May 1970, detailing his knowledge of the plan to import weapons after the outbreak of sectarian violence in the North.
The deletions are marked in the handwriting of the late Declan Quigley, a senior official in the office of the Attorney General and member of the prosecution legal team.
In his original statement, Col Hefferon not only detailed the involvement of some defendants in the trial but also indicated that Mr Gibbons was aware of the plan to import arms.
Mr Gibbons was a key witness for the prosecution, so evidence that he himself was aware of the plan could have fatally undermined the prosecution case.
The discovery two years ago of a copy of the original statement with deletions marked in the handwriting of the secretary of the Department of Justice, the late Mr Peter Berry, suggested high-level Civil Service and possibly political involvement in the changes. Date stamps on the statement indicated it was seen by Mr Berry the day after it was made and by Mr O'Malley the day after that.
It was suggested in the RTE Prime Time programme which revealed the contents of the original statement that the changes could have been made before the prosecution lawyers saw the statement. If true, this would have meant that the prosecution team was unaware that Col Hefferon had in fact implicated Mr Gibbons.
However, the newly discovered copy of the Hefferon statement with Mr Quigley's handwriting on it shows that the prosecution team did indeed have access to the unedited version before the trial. It was they who did the final editing before the trial.
Sources said this week that further documents may emerge through the National Archives in this or future years, revealing who decided upon this "editorial policy".
Historians are also hoping for papers that would shed further light on the connection - if any - between the markings made by Mr Berry on the day after the colonel made his statement and the version edited by the State's legal team that ultimately was used in the trial.